This invention relates to displays.
The recent application of flat panel displays in portable electronic products has renewed interest in developing low cost, high performance technologies such as flat cathode ray tubes and field-emitter displays (FEDs). FED panels are of particular interest because they can exhibit the most desirable aspects of a CRT. That is, they are emissive, they can have a full range of colours and grey scale, and have a wide viewing angle and high resolution. In addition, this display technology is thin, light-weight, rugged, is matrix addressed and requires only low power. Furthermore, FED panels will not generate X-rays if operated at low to moderate (5 kV) anode voltages.
In 1991 a research team at LETI, lead by Robert Meyer demonstrated the first colour flat panel based on the microtip Field Emission Array (FEA) proposed by Cap Spindt at SRI in 1968. This display used a large number of very fine micro-tip cold cathodes as the sources of electrons. Each pixel can be addressed independently to release electrons which are accelerated towards a phosphor-coated anode faceplate positioned above the FEA, to produce a cathodoluminescent image. Sub-micron sized microtips and concentric grids are necessary to achieve locally enhanced electric field strengths of up to 500V/micron at gate voltages of 40 to 80 volts from metal cathodes which have a work function of 4.5 eV.
Low cost production of large area panels using this micro-tip triode structure has proven to be difficult because of the need to fabricate a high density of microscopically sharp tips to obtain the best emission efficiency. Sub-micron features must be fabricated over large areas, which dramatically increases the cost of capital equipment. Existing, vertically-gated microtip field emitter arrays (FEA) also suffer from significant current leakage between the gate and emitter electrode through the dielectric film separating them. Such leakage occurs due to the high field strengths generated between the gate and emitter lines necessary to cause emission from the gated metal tips. Current leakage is a significant problem in FEDs because, in addition to the dissipative losses, the capacitive load introduced across the dielectric can affect the speed of response of the emitter when it is being addressed. This leakage effect also complicates the drive circuits needed.
It is an object of the present invention to provide an alternative display.
According to one aspect of the present invention there is provided a display including a cathode emitter base plate having a plurality of gated, cathode structures of linear form, each cathode structure having a pair of electrodes separated from one another by a gap and having a plurality of electron field emitter sites spaced along its length, such that when a cathode structure is addressed with a voltage, all of the emitter sites along the addressed cathode are gated to conduct current across the gap, the display including a screen separated from the base plate by a vacuum gap, and the screen having a fluorescent layer and having a plurality of addressable anode stripes extending transversely of the cathode structures such that a voltage applied to an anode stripe causes a portion of the electron current at a conducting emitter site below the stripe to be redirected towards the screen to cause illumination of a pixel on the fluorescent layer.
Each electrode of the cathode structures preferably includes a plurality of teeth projecting from opposite sides towards an adjacent electrode, the electron emitter sites being located between teeth of adjacent electrodes. Each electron emitter site is preferably provided by a dot of material bridging the gap between the pairs of electrodes of the cathode structure. The material may be selected from a group comprising: semiconducting diamond, nanotube carbon, gallium nitride and metal oxides. The anode stripes are preferably transparent to light emitted by the fluorescent layer, which is preferably formed on the anode stripes. The fluorescent layer may include regions of phosphors that fluoresce with different colours arranged such that a full colour picture can be displayed. The screen may have a black material between the fluorescent pixels.
A display according to the present invention will now be described, by way of example, with reference to the accompanying drawings.